Reflective film coated substrate, mask blank, reflective mask, and semiconductor device manufacturing method

ABSTRACT

A reflective film coated substrate includes a substrate having two main surfaces opposite to each other and end faces connected to outer edges of the two main surfaces; and a reflective film formed on one of the main surfaces and extending onto at least part of the end faces. The reflective film on the main surface has a multilayer structure including low refractive index layers and high refractive index layers alternately formed. The reflective film which extends onto the end faces has a single-layer structure containing a first element higher in content than any other element in the low refractive index layers and a second element higher in content than any other element in the high refractive index layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/008,949, filed Sep. 1, 2020, which claims priority to Japanese PatentApplication No. 2019-159908 filed Sep. 2, 2019 and Japanese PatentApplication No. 2020-117891 filed Jul. 8, 2020, the contents of whichare incorporated herein by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to a reflective film coated substrate, a maskblank, and a reflective mask which are for use in EUV lithography, andto a method for manufacturing a semiconductor device.

BACKGROUND ART

Generally, in a manufacturing process of a semiconductor device, a finepattern is formed using a photolithography method. In forming the finepattern, a number of transfer masks called photomasks are commonly used.The transfer mask generally comprises a transparent glass substrate anda fine pattern formed thereon and made of a metal thin film or the like.In manufacture of the transfer mask, the photolithography method is usedalso.

In recent years, in a semiconductor industry, higher integration of asemiconductor device requires a fine pattern exceeding a transfer limitin a related-art photolithography method using ultraviolet light. Inorder to enable formation of such a fine pattern, EUV lithography, whichis an exposure technology using extreme ultra violet (hereinafterreferred to as “EUV”) light, is considered promising. Herein, the EUVlight means light in a wavelength band of a soft X-ray region or avacuum ultraviolet region, specifically, light having a wavelength in arange of about 0.2 nm to about 100 nm. As a mask for use in the EUVlithography, a reflective mask is proposed. The reflective maskcomprises a substrate, a multilayer reflective film formed on thesubstrate to reflect exposure light, and an absorber film formed as apattern on the multilayer reflective film to absorb the exposure light(for example, see WO2009/116348A1).

SUMMARY OF THE DISCLOSURE Problem to be Solved by the Disclosure

In recent years, with an increasing demand for miniaturization in alithography process, problems in the lithography process become salientand noticeable. One of the problems is adhesion of contamination to amirror or a mask in an exposure device due to EUV light irradiation inan EUV lithography process.

In order to resolve the above-mentioned problem, a technique ofsuppressing the adhesion of contamination during EUV exposure by fillingan interior of an exposure chamber with a hydrogen atmosphere such ashydrogen radicals, a cleaning method for removing contamination byhydrogen plasma, and so on come into use.

However, in case where the above-mentioned techniques are applied, therearises a new problem of occurrence of so-called “blisters” caused byhydrogen intruding into a film of the mask and agglomerating to generatebulges of the film. When the film bulges and raptures due to occurrenceof the blisters, contamination by dust generation is caused in theinterior of the exposure chamber. It has been found out that hydrogenintruding into the film is easily captured at an interface between thefilm and another film, although depending on a material of the film, andthe blisters easily occur at the interface between the two layeredfilms.

In the meanwhile, the reflective mask used in the EUV lithographycomprises the reflective film formed on the substrate to reflect theexposure light (EUV light). The reflective film is a multilayer filmhaving a structure in which low refractive index layers and highrefractive index layers are alternately formed. The reflective film isformed on one main surface of the substrate, for example, by sputtering.In this case, the reflective film is not only formed on the one mainsurface of the substrate but also extends onto end faces of thesubstrate to be deposited thereon. If the reflective film deposited onthe end faces of the substrate has a multilayer structure similar tothat of the reflective film formed on the main surface, a risk ofoccurrence of the blisters is increased at an interface present in themultilayer film.

It is therefore a first aspect of this disclosure to provide areflective film coated substrate and a mask blank which are capable ofreducing occurrence of blisters, in particular, in a reflective filmwhich extends onto end faces of a substrate.

It is a second aspect of this disclosure to provide a reflective maskwhich is manufactured using the mask blank mentioned above and which iscapable of reducing occurrence of blisters, in particular, in areflective film which extends onto end faces of a substrate.

It is another aspect of this disclosure to provide a method formanufacturing a semiconductor device using the above-mentionedreflective mask.

Means to Solve the Problem

In order to resolve the above-mentioned problem, the present inventorscontinued diligent studies, focusing on the structure of the reflectivefilm spreading over and adhered onto the end faces of the substrate whenthe reflective film is formed on the main surface of the substrate. As aresult, this disclosure has been completed.

Specifically, this disclosure has the following configurations in orderto resolve the above-mentioned problem.

(Configuration 1)

A reflective film coated substrate comprising:

a substrate having:

-   -   two main surfaces opposite from each other; and    -   end faces connected to outer edges of the two main surfaces; and

a reflective film formed on one of the main surfaces as a multilayerstructure comprising low refractive index layers and high refractiveindex layers alternately formed,

wherein a content (atomic %) of a first element in the low refractiveindex layers is higher than a content (atomic %) of any other element inthe low refractive index layers, and a content (atomic %) of a secondelement in the high refractive index layers is higher than a content(atomic %) of any other element in the high refractive index layers, thesecond element being a different element from the first element, and

wherein the reflective film extends onto the end faces as a single layerthat contains the first element and the second element.

(Configuration 2)

The reflective film coated substrate according to Configuration 1,wherein, in the reflective film that extends onto the end faces, a ratioof the content (atomic %) of the first element to the total content(atomic %) of the first element and the second element is less than 0.4.

(Configuration 3)

The reflective film coated substrate according to Configuration 1,wherein the film thickness of the reflective film that extends onto theend faces is smaller than the film thickness of the reflective filmformed on the main surface.

(Configuration 4)

The reflective film coated substrate according to Configuration 1,wherein the first element is molybdenum and the second element issilicon.

(Configuration 5)

The reflective film coated substrate according to Configuration 1,wherein the reflective film that extends onto the end faces has surfaceroughness (root mean square roughness) Rq of 1.5 nm or more.

(Configuration 6)

A mask blank comprising:

a substrate having:

-   -   two main surfaces opposite from each other; and    -   end faces connected to outer edges of the two main surfaces; and

a reflective film formed on one of the main surfaces as a multilayerstructure comprising low refractive index layers and high refractiveindex layers alternately formed; and

a pattern-forming thin film formed on the reflective film,

wherein a content (atomic %) of a first element in the low refractiveindex layers is higher than a content (atomic %) of any other element inthe low refractive index layers, and a content (atomic %) of a secondelement in the high refractive index layers is higher than a content(atomic %) of any other element in the high refractive index layers, thesecond element being a different element from the first element, and

wherein the reflective film extends onto the end faces as a single layerthat contains the first element and the second element.

(Configuration 7)

The mask blank according to Configuration 6, wherein, in the reflectivefilm that extends onto the end faces, a ratio of the content (atomic %)of the first element to the total content (atomic %) of the firstelement and the second element is less than 0.4.

(Configuration 8)

The mask blank according to Configuration 6, wherein the film thicknessof the reflective film that extends onto the end faces is smaller thanthe film thickness of the reflective film formed on the main surface.

(Configuration 9)

The mask blank according to Configuration 6, wherein the first elementis molybdenum and the second element is silicon.

(Configuration 10)

The mask blank according to Configuration 6, wherein the reflective filmthat extends onto the end faces has surface roughness (root mean squareroughness) Rq of 1.5 nm or more.

(Configuration 11)

A reflective mask comprising:

a substrate having:

-   -   two main surfaces opposite to each other; and    -   end faces connected to outer edges of the two main surfaces;

a reflective film formed on one of the main surfaces as a multilayerstructure comprising low refractive index layers and high refractiveindex layers alternately formed; and

a thin film formed on the reflective film and having a transfer pattern;

wherein a content (atomic %) of a first element in the low refractiveindex layers is higher than a content (atomic %) of any other element inthe low refractive index layers, and a content (atomic %) of a secondelement in the high refractive index layers is higher than a content(atomic %) of any other element in the high refractive index layers, thesecond element being a different element from the first element, and

wherein the reflective film extends onto the end faces as a single layerthat contains the first element and the second element.

(Configuration 12)

The reflective mask according to Configuration 11, wherein, in thereflective film that extends onto the end faces, a ratio of the content(atomic %) of the first element to the total content (atomic %) of thefirst element and the second element is less than 0.4.

(Configuration 13)

The reflective mask according to Configuration 11, wherein the filmthickness of the reflective film that extends onto the end faces issmaller than the film thickness of the reflective film formed on themain surface.

(Configuration 14)

The reflective mask according to Configuration 11, wherein the firstelement is molybdenum and the second element is silicon.

(Configuration 15)

The reflective mask according to Configuration 11, wherein thereflective film that extends onto the end faces has surface roughness(root mean square roughness) Rq of 1.5 nm or more.

(Configuration 16)

A method for manufacturing a semiconductor device, comprisingtransferring, by exposure, a transfer pattern onto a resist film on asemiconductor substrate by using the reflective mask according toConfiguration 11.

Effect of the Disclosure

According to this disclosure, the reflective film on the end faces hasthe single-layer structure containing the first element greater incontent than any other element in the low refractive index layers andthe second element greater in content than any other element in the highrefractive index layers. It is therefore possible to provide thereflective film coated substrate and the mask blank which are capable ofreducing occurrence of blisters, in particular, in the reflective filmwhich extends onto the end faces of the substrate.

Moreover, according to this disclosure, it is possible to provide, byusing the above-mentioned mask blank, the reflective film capable ofreducing occurrence of blisters, in particular, in the reflective filmwhich extends onto the end faces of the substrate.

Furthermore, according to this disclosure, it is possible to provide amethod for manufacturing a semiconductor device by using theabove-mentioned mask blank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view for illustrating a structure of a reflectivefilm coated substrate according to one embodiment of this disclosure;

FIG. 2 is a sectional view for illustrating a film structure of areflective film illustrated in FIG. 1 ;

FIG. 3 is a sectional view for illustrating a structure of a mask blankaccording to one embodiment of this disclosure; and

FIG. 4 is a sectional view for illustrating a structure of a reflectivemask manufactured by using the mask blank according to this disclosure.

DESCRIPTION OF THE EMBODIMENTS

Now, embodiments of this disclosure will be described in detail.

[Reflective Film Coated Substrate]

At first, description will be made of a reflective film coated substrateaccording to an embodiment of this disclosure.

FIG. 1 is a sectional view for illustrating a structure of thereflective film coated substrate according to one embodiment of thisdisclosure.

As illustrated in FIG. 1 , the reflective film coated substrate 10according to the one embodiment of this disclosure comprises a substrate1 and a reflective film 2.

The substrate 1 has two main surfaces 1 a and 1 b opposite to eachother, and end faces 1 c and 1 d connected to outer edges of the twomain surfaces 1 a and 1 b.

The substrate 1 used in this disclosure has a rectangular shape as awhole and therefore has four end faces connected to the outer edges ofthe two main surfaces 1 a and 1 b. In this disclosure, the “end faces”refer to those four end faces. In the sectional view of FIG. 1 , amongthe four end faces, only the two end faces 1 c and 1 d opposite to eachother in left and right directions of the substrate 1 are illustrated.Although not shown in the figure, the substrate 1 has two other endfaces opposite to each other in forward and backward directions of thesubstrate 1. Accordingly, the reflective film 2 extends onto at leastpart of the two other end faces not shown in FIG. 1 . In the following,this embodiment will be described as regards the two end faces 1 c and 1d for convenience of description but similar description also applies tothe two other end faces opposite to each other.

The reflective film 2 is formed over the whole of the one main surface 1a and extends onto at least part of the end faces 1 c and 1 d.Specifically, the reflective film 2 includes a reflective film 2 aformed on the main surface 1 a and reflective films 2 c and 2 d whichextend onto the end faces 1 c and 1 d, respectively.

As illustrated in FIG. 2 , the reflective film 2 a formed on the mainsurface 1 a has a multilayer structure in which low refractive indexlayers 21 and high refractive index layers 22 are alternately formed. Inthe present specification, a low refractive index and a high refractiveindex are based on a refractive index with respect to a wavelength ofEUV light.

Each of the reflective films 2 c and 2 d which extend onto the end faces1 c and 1 d has a single-layer structure containing a first element inthe low refractive index layers 21 and a second element in the highrefractive index layers 22. A content (atomic %) of the first element inthe low refractive index layers 21 is higher than a content (atomic %)of any other element in the low refractive index layers 21, and acontent (atomic %) of the second element in the high refractive indexlayers 22 is higher than a content (atomic %) of any other element inthe high refractive index layers 22. The second element is a differentelement from the first element.

Herein, the first element in the low refractive index layers 21preferably has a content more than 50 atomic %, more preferably 70atomic % or more, further preferably 90 atomic % or more. Similarly, thesecond element in the high refractive index layers 22 preferably has acontent more than 50 atomic %, more preferably 70 atomic % or more,further preferably 90 atomic % or more.

In another aspect, each of the reflective films 2 c and 2 d which extendonto the end faces 1 c and 1 d may have a single-layer structurecomprising a material which is a mixture of a main constituent elementof the low refractive index layers 21 and a main constituent element ofthe high refractive index layers 22.

Herein, the “main constituent element” of the low refractive indexlayers 21 (high refractive index layers 22) refer to a constituentelement or elements except those elements having a total content lessthan 5 atomic % in the low refractive index layers 21 (high refractiveindex layers 22). Thus, in this case, the total content of the “mainconstituent element” in the low refractive index layers 21 (highrefractive index layers 22) is 95 atomic % or more. Therefore, even ifthe formed reflective film contains impurity components contained in atarget material and/or impurity components derived from a structure suchas a shield in a film-forming chamber, those impurity components are notincluded in the main constituent element of the low refractive indexlayers 21 or the high refractive index layers 22.

In case of EUV exposure, the substrate 1 preferably has a low thermalexpansion coefficient in a range of 0±1.0×10⁻⁷/° C., more preferably ina range of 0±0.3×10⁻⁷/° C. in order to prevent deformation of a patterndue to heat during exposure. As a material having the low thermalexpansion coefficient in the above-mentioned range, for example, aSiO₂—TiO₂-based glass, multicomponent glass ceramics, and so on may beused.

In case where a glass substrate of the above-mentioned material is usedas the substrate 1, the main surface of the glass substrate on which atransfer pattern is to be formed is surface-treated so as to have highflatness in view of obtaining at least transfer accuracy and positionalaccuracy. In case of the EUV exposure, the main surface of the glasssubstrate on which the transfer pattern is to be formed preferably hasflatness of 0.1 μm or less, more preferably 0.05 μm or less, in an areaof 132 mm×132 mm or an area of 142 mm×142 mm. The other main surface ofthe glass substrate opposite from the main surface on which the transferpattern is to be formed is a surface to be held by electrostaticchucking when the glass substrate is set in an exposure device, and hasflatness of 1 μm or less, preferably 0.5 μm or less, in an area of 142mm×142 mm.

The reflective film 2 is a multilayer film in which the low refractiveindex layers 21 and the high refractive index layers 22 are alternatelyformed. Generally, the multilayer film is used which comprises thinfilms of a heavy element or a compound thereof and thin films of a lightelement or a compound thereof alternately formed as layers in about 40to 60 periods.

For example, as the reflective film for the EUV light having awavelength of 13 to 14 nm, a Mo/Si periodic multilayer film comprisingMo films (low refractive index layers) and Si films (high refractiveindex layers) are alternately formed in 40 periods or more is preferablyused. Besides, as the multilayer reflective film for use in a wavelengthregion of the EUV light, there are a Ru/Si periodic multilayer film, aMo/Be periodic multilayer film, a Mo-compound/Si-compound periodicmultilayer film, a Si/Nb periodic multilayer film, a Si/Mo/Ru periodicmultilayer film, a Si/Mo/Ru/Mo periodic multilayer film, a Si/Ru/Mo/Ruperiodic multilayer film, and so on. Depending on an exposurewavelength, the material of the reflective film 2 may appropriately beselected. The reflective film 2 may be formed by, for example, ion beamsputtering or atomic layer deposition (ALD).

In order to resolve the above-mentioned problem, the present inventorsconducted diligent studies, focusing on the structure of the reflectivefilm spread over and adhered to the end faces of the substrate when thereflective film is formed on the main surface of the substrate. As aresult, it has been found out that the reflective film adhered to theend faces of the substrate do not require a reflecting function for theexposure light at all and, therefore, need not have a multilayerstructure similar to the reflective film formed on the main surface ofthe substrate. Furthermore, it has been found out that, in view ofreducing occurrence of blisters, being a film having a single-layerstructure without any interface in the film leads to solution of theproblem.

In the reflective film coated substrate 10 according to this embodimentmentioned above, the reflective film 2 c (or 2 d) which extends onto theend face 1 c (or 1 d) of the substrate 1 when the reflective film 2 isformed on the main surface 1 a of the substrate 1, has the single-layerstructure containing the first element (for example, molybdenum) and thesecond element (for example, silicon). The reflective film 2 c (or 2 d)is formed by mixing and dispersing at least the first element and thesecond element. The above-mentioned reflective film 2 c (or 2 d) is afilm having the single-layer structure without any clear interface.

In another aspect, the reflective film 2 c (or 2 d) is formed by mixingand dispersing film forming materials of the reflective film 2, i.e.,the main constituent element (for example, molybdenum) of the lowrefractive index layers 21 and the main constituent element (forexample, silicon) of the high refractive index layers 22, and is a filmof a single-layer structure without an interface.

Accordingly, even when the technique of reducing adhesion ofcontamination by hydrogen radicals or hydrogen plasma is applied duringthe EUV exposure using a mask blank and a reflective mask, which willlater be described, manufactured by using the reflective film coatedsubstrate 10 in this embodiment, it is possible to significantly lower arisk of occurrence of the blisters.

The reflective film coated substrate according to this disclosure has astructure in which at least the reflective film 2 for reflecting theexposure light (for example, the EUV light) is formed on the substrate1, as illustrated in FIG. 1 . In addition, the reflective film coatedsubstrate according to this disclosure may have a structure furthercomprising other film or films such as an underlayer, a protective filmformed on the reflective film 2, and so on, as will later be described.

In the substrate 1 according to this embodiment illustrated in FIG. 1 ,the end faces connected to the outer edges of the two main surfaces 1 aand 1 b opposite to each other are substantially orthogonal to the twomain surfaces 1 a and 1 b. In some cases, the end faces of the substratehave chamfered faces. Specifically, when each of the end faces of thesubstrate has a side surface substantially orthogonal to the two mainsurfaces, and two chamfered faces connecting the side surface and theouter edges of the two main surfaces and when the reflective film 2 isformed on at least part of the side surface and the chamfered faces, the“reflective film on the end faces” refers to the reflective film whichextends onto at least part of the side surface and the chamfered faces.

Similarly, in the reflective film coated substrate 10 in thisembodiment, it is preferable that the ratio (hereinafter referred to asthe L/(L+H) ratio) of the content (L) [atomic %] to the total content(L+H) [atomic %] is preferably smaller than 0.4. In this case, thecontent (L) [atomic %] represents a content of the first elementcontained in the reflective film 2 c (or 2 d). The content (H) [atomic%] represents a content of the second element contained in thereflective film 2 c (or 2 d). The total content (L+H) [atomic %]represents a total content of the content (L) and the content (H).

The first element higher in content than any other element in the lowrefractive index layers 21 (main constituent element of the lowrefractive index layers 21) is, for example, molybdenum. The secondelement higher in content than any other element in the high refractiveindex layers 22 (main constituent element in the high refractive indexlayers 22) is, for example, silicon. In view of a reflectance, in thereflective film 2 a formed on the main surface 1 a of the substrate 1, aratio of the total film thickness of the low refractive index layers 21and the total film thickness of the high refractive index layers 22 ispreferably 4:6 (i.e., the L/(L+H) ratio in the whole of the reflectivefilm 2 a formed on the main surface 1 a is equal to 0.4).

On the other hand, the reflective film 2 c (or 2 d) which extends ontothe end face 1 c (or 1 d) in this embodiment is a film of a single-layerstructure containing the first element and the second element.Alternatively, the reflective film 2 c (or 2 d) is a film of asingle-layer structure comprising a mixture of the main constituentelement of the low refractive index layers 21 and the main constituentelement of the high refractive index layers 22. As the element havingthe highest content in the low refractive index layer 21 (mainconstituent element in the low refractive index layers 21), a transitionmetal (for example, molybdenum) is often used. The first element higherin content than any other element in the low refractive index layers 21(main constituent element of the low refractive index layers 21) is lowin chemical resistance and easily dissolved from the single-layer filmas compared with the second element higher in content than any otherelement in the high refractive index layers 22 (main constituent elementof the high refractive index layers 22). In view of the above, theL/(L+H) ratio in the reflective film 2 c (or 2 d) which extends onto theend face 1 c (or 1 d) is preferably smaller than the L/(L+H) ratio inthe entire reflective film 2 a formed on the main surface 1 a. TheL/(L+H) ratio in the reflective film 2 c (or 2 d) which extends onto theend face 1 c (or 1 d) is preferably 0.33 or less, more preferably 0.3 orless. In particular, in case where the first element higher in contentthan any other element in the low refractive index layers 21 (mainconstituent element of the low refractive index layers 21) is atransition metal and the second element higher in content than any otherelement in the high refractive index layers 22 (main constituent elementof the high refractive index layers 22) is silicon, chemical resistanceis improved when the content of the transition metal is smaller thanthat given by the ratio of transition metal:silicon=1:2 which is astoichiometrically stable ratio of a transition metal silicide basedmaterial.

The film thickness of the reflective film 2 which extends onto the endface 1 c (or 1 d) (film thickness of the reflective film 2 c (or 2 d))is desirably smaller than the film thickness of the reflective film 2formed on the main surface 1 a (film thickness of the reflective film 2a). If the film thickness of the reflective film 2 which extends ontothe end face 1 c (or 1 d) is greater, a risk of dust generation due tofilm peeling at the end face 1 c (or 1 d) of the substrate 1 isincreased. Furthermore, an interface is formed in the reflective film 2c (or 2 d) with high possibility. The ratio of the film thickness of thereflective film 2 c (or 2 d) with respect to the film thickness of thereflective film 2 a is preferably 0.4 or less, more preferably 0.3 orless.

The surface roughness (root mean square roughness) Rq of the reflectivefilm 2 c (or 2 d) which extends onto the end face 1 c (or 1 d) is, forexample, equal to 1.5 nm or more. Preferably, the surface roughness(root mean square roughness) Rq of the reflective film 2 c (or 2 d) is 2nm or more. On the other hand, the surface roughness (root mean squareroughness) Rq of the reflective film 2 c (or 2 d) preferably has a filmthickness of 3 nm or less.

As described above, in the reflective film coated substrate 10 accordingto this embodiment, the reflective film 2 c (or 2 d) extends onto theend face 1 c (or 1 d) of the substrate 1 when the reflective film 2 isformed on the main surface 1 a of the substrate 1 has a single-layerstructure containing the first element (for example, molybdenum) and thesecond element (for example, silicon). The reflective film 2 c (or 2 d)is a film of the single-layer structure without any clear interface.

In another aspect, in the reflective film coated substrate 10 accordingto this embodiment, the reflective film 2 c (or 2 d) extends onto theend face 1 c (or 1 d) of the substrate 1 when the reflective film 2 isformed on the main surface 1 a of the substrate 1 is a film of asingle-layer structure in which the main constituent element (forexample, molybdenum) of the low refractive index layers 21 that is thefilm-forming material of the reflective film 2 and the main constituentelement (for example, silicon) of the high refractive index layers 22that is the film-forming material of the reflective film 2 are mixed anddispersed without any interface.

Therefore, even if the technique of reducing the adhesion ofcontamination by hydrogen radicals or hydrogen plasma is applied duringthe EUV exposure using a reflective mask manufactured by using thereflective film coated substrate 10 according to this embodiment, a riskof occurrence of the blisters can significantly be reduced.

[Mask Blank]

Next, description will be made of a mask blank according to thisdisclosure.

The mask blank according to this disclosure comprises a substrate havingtwo main surfaces opposite to each other and end faces connected toouter edges of the two main surfaces, a reflective film formed on one ofthe main surfaces and extending onto at least part of the end faces, anda pattern-forming thin film formed on the reflective film. Thereflective film formed on the main surface has a structure comprisinglow refractive index layers and high refractive index layers alternatelyformed. The reflective film which extends onto the end faces has asingle-layer structure containing a first element in the low refractiveindex layers and a second element in the high refractive index layers. Acontent (atomic %) of the first element in the low refractive indexlayers is higher than a content (atomic %) of any other element in thelow refractive index layers, and a content (atomic %) of the secondelement in the high refractive index layers is higher than a content(atomic %) of any other element in the high refractive index layers. Thesecond element is a different element from the first element.

In another aspect, a mask blank according to this disclosure comprises asubstrate, a reflective film, and a pattern-forming thin film. Thesubstrate has two main surfaces opposite to each other and end facesconnected to outer edges of the two main surfaces. The reflective filmis formed on one of the main surfaces and extends onto at least part ofthe end faces. The reflective film formed on the main surface has astructure comprising low refractive index layers and high refractiveindex layers alternately formed. The reflective film on the end faceshas a single-layer structure containing a material which is a mixture ofa main constituent element of the low refractive index layers and a mainconstituent element of the high refractive index layers. Thepattern-forming thin film is formed on the reflective film.

The mask blank according to this disclosure essentially has a filmstructure in which at least the reflective film for reflecting exposurelight (for example, EUV light) and the pattern-forming thin film areformed on the substrate. The mask blank may have a structure furthercomprising other films, such as an underlayer, a protective film formedon the reflective film, an etching mask film formed on thepattern-forming thin film, which will later be described. Thepattern-forming thin film may be an absorber film for absorbing the EUVlight. Alternatively, the pattern-forming thin film may be a phase shiftfilm having a function of transmitting the EUV light at a predeterminedtransmittance and a function of causing a predetermined phase differencebetween the EUV light passing through the thin film, reflected at aninterface between the thin film and the reflective film, and emittedfrom the thin film again and the EUV light passing through vacuum anddirectly reflected by the reflective film.

The mask blank according to this disclosure is also characterized inthat the reflective film is formed on one of the main surfaces andextends onto at least part of the end faces, that the reflective film onthe main surface has a structure comprising the low refractive indexlayers and the high refractive index layers alternately formed, that thereflective film on the end faces has a single-layer structure containinga material which is a mixture of the main constituent element of the lowrefractive index layers and the main constituent element of the highrefractive index layers. These characteristics are already explainedabove in the section entitled Reflective Film Coated Substrate andrepeated description is omitted herein.

In the mask blank according to this disclosure, the following mattersare similar to those in case of the Reflective Film Coated Substratementioned above and description thereof will be omitted herein.

(1) The ratio (L/(L+H) ratio) of the content (L) [atomic %] to the totalcontent (L+H) [atomic %) is smaller than 0.4.

(2) The film thickness of the reflective film which extends onto the endfaces is smaller than the film thickness of the reflective film formedon the main surface.

(3) The low refractive index layers are formed of a material containing,for example, molybdenum whereas the high refractive index layers areformed of a material containing, for example, silicon.

(4) The surface roughness (root mean square roughness) Rq of thereflective film which extends onto the end faces is 1.5 nm or more.

(5) Other matters related to (1) to (4).

FIG. 3 is a sectional view for illustrating a structure of the maskblank according to one embodiment of this disclosure. In FIG. 3 , partssimilar to those in FIG. 1 are designated by the same referencenumerals.

The mask blank 20 according to the one embodiment of this disclosureillustrated in FIG. 3 comprises a substrate 1, a reflective film 2formed on the substrate 1 to reflect, for example, EUV light, aprotective film 3, and a pattern-forming thin film 4. In thisembodiment, description will be made of a case where the pattern-formingthin film 4 is an absorber film for absorbing exposure light (forexample, EUV light).

In case of EUV exposure, a glass substrate, such as a SiO₂—TiO₂-basedglass, having a low thermal expansion coefficient is preferably used asthe substrate 1 as described above. However, in such glass substrate, itmay sometimes be difficult to achieve, as surface roughness, highflatness of 0.1 nm or less in RMS (Root Mean Square) roughness (Rq) byprecision polishing. Therefore, for the purpose of reducing the surfaceroughness of the glass substrate or reducing defects on a surface of theglass substrate, it is preferable to form the underlayer (not shown) onthe surface of the glass substrate (the above-mentioned substrate 1). Asa material of the underlayer, a light transparency with respect to theexposure light is not required and a material which would be high inflatness and excellent in quality when a surface of the underlayer isprecision-polished is preferably selected. For example, Si or a siliconcompound containing Si (for example, SiO₂, SiON, and so on) ispreferably used because high flatness is obtained and the quality isexcellent when precision-polishing is carried out. As the material ofthe underlayer, Si is particularly preferable.

Preferably, the surface of the underlayer is precision-polished so as tohave flatness required as a mask blank substrate. It is desired that thesurface of the underlayer is precision-polished to have surfaceroughness of 0.15 nm or less, particularly preferably 0.1 nm or less inroot mean square roughness (Rq). Taking into account an influence on thesurface of the reflective film 2 formed on the underlayer, it is desiredthat the surface of the underlayer is precision-polished so that, in therelationship between the root square mean roughness and the maximumsurface roughness, Rmax/Rq is 2 to 10, particularly preferably 2 to 8.The film thickness of the underlayer is preferably in a range of, forexample, 75 nm to 300 nm.

Generally, for the purpose of protecting the reflecting film 2 duringpatterning or pattern repairing of the pattern-forming thin film 4, theprotective film 3 is desirably formed between the reflective film 2 andthe pattern-forming thin film 4 as in this embodiment.

The protective film 3 is formed on the reflective film 2 in order toprotect the reflective film 2 from dry etching and cleaning in amanufacturing process of a reflective mask 30 which will later bedescribed. Furthermore, the protective film 3 may protect the reflectivefilm 2 during black defect repair (EB defect repair) of a transferpattern using an electron beam (EB). The protective film 3 may have alayered structure of three layers or more. For example, the protectivefilm 3 may have a structure comprising a lowermost layer, an uppermostlayer, and an intermediate layer interposed between the lowermost layerand the uppermost layer. Each of the lowermost layer and the uppermostlayer is formed of a metal containing ruthenium (Ru). The intermediatelayer is a metal layer of a metal except Ru or an alloy layer of a metalexcept Ru. The protective film 3 is formed of, for example, a materialcontaining Ru as a main component. The material containing Ru as a maincomponent may be Ru elemental metal or an Ru alloy containing Ru andtitanium (Ti), niobium (Nb), molybdenum (Mo), zirconium (Zr), yttrium(Y), boron (B), lanthanum (La), cobalt (Co), and/or rhenium (Re) addedthereto. The material of the protective film 3 may further containnitrogen. The protective film 3 is effective in case where thepattern-forming thin film 4 is patterned by dry etching using a Cl-basedgas.

The thickness of the protective film 3 is not particularly limited asfar as the function as the protective film 3 is satisfied. In view ofreflectance for the EUV light, the thickness of the protective film 3 ispreferably 1.0 nm to 8.0 nm, more preferably 1.5 nm to 6.0 nm.

The protective film 3 may be formed on the reflective film 2 c (or 2 d)which extends onto the end face 1 c (or 1 d) but is not essential. Thereflective film 2 c (or 2 d) on the end face 1 c (or 1 d) is, in manycases, not surmounted by or not coated with the pattern-forming thinfilm 4, and is hardly affected by dry etching or EB defect repair.Furthermore, the reflective film 2 c (or 2 d) is a film of asingle-layer structure comprising a material which is a mixture of themain constituent element of the low refractive index layers and the mainconstituent element of the high refractive index layers and is high inresistance against the dry etching or the EB defect repair, includingchemical resistance. From the above, the necessity for forming theprotective film 3 on the reflective film 2 c (or 2 d) is low. A surfacelayer (for example, a region from the surface to a depth or 5 nm orless) of the reflective film 2 c (or 2 d) may have a composition with aconstituent element of the protective film 3 mixed therein.

In the mask blank 20 according to this embodiment, the pattern-formingthin film 4 may be a single-layer film or a multilayer film comprising aplurality of films. In case of the single-layer film, there is anadvantage that the number of steps during manufacture of the mask blankcan be reduced and production efficiency is increased. In case of themultilayer film, it is possible to appropriately set an optical constantand a film thickness so that the thin film of an upper layer serves asan antireflection film during inspection of mask pattern defects usinglight. This improves inspection sensitivity during inspection of maskpattern defects using light. If a film added with oxygen (O), nitrogen(N), and so on which improve oxidation resistance is used as the thinfilm of the upper layer, stability with time is improved.

A material of the pattern-forming thin film 4 is not particularlylimited as far as the material has a function of absorbing the EUV lightand is processable by etching or the like (preferably etchable by dryetching using a chlorine (CI) based gas and/or a fluorine (F) basedgas). As the material having such a function, elemental tantalum (Ta) ora material containing Ta may preferably be used.

The material containing Ta may be, for example, a material containing Taand B, a material containing Ta and N, a material containing Ta, B, andat least one of O and N, a material containing Ta and Si, a materialcontaining Ta, Si, and N, a material containing Ta and Ge, a materialcontaining Ta, Ge, and N, a material containing Ta and Pd, a materialcontaining Ta and Ru, a material containing Ta and Ti, and so on.

For example, the pattern-forming thin film 4 may be formed of a materialcontaining at least one selected from a group including elemental Ni, amaterial containing Ni, elemental Cr, a material containing Cr,elemental Ru, a material containing Ru, elemental Pd, a materialcontaining Pd, elemental Mo, and a material containing Mo.

The pattern-forming thin film 4 may be formed by, for example,sputtering. The film thickness of the pattern-forming thin film ispreferably within a range of, for example, 25 nm to 70 nm.

On the pattern-forming thin film 4, an etching mask film may beprovided. By providing the etching mask film, a resist film formed onthe absorber film (pattern-forming thin film) upon patterning thepattern-forming thin film 4 can be reduced in film thickness. Therefore,it is possible to form a fine pattern in the pattern-forming thin film 4with high accuracy.

The etching mask film is formed of a material having etching selectivitywith respect to the pattern-forming thin film 4. In case where theabsorber film (pattern-forming thin film) is formed of theabove-mentioned tantalum-based material, the etching mask film ispreferably formed of, for example, a chromium-based material. Thechromium-based material may be, for example, elemental chromium (Cr) ora chromium compound (chromium oxide, chromium nitride, chromiumoxynitride, chromium carbide, and so on).

The etching mask film may be formed by, for example, sputtering. Thefilm thickness of the etching mask film preferably falls within a rangebetween 5 nm and 15 nm.

The above-described mask blank 20 according to this embodiment asillustrated in FIG. 3 may be manufactured by sequentially forming, onthe substrate 1, the reflective film 2, the protective film 3, and thepattern-forming thin film 4. If necessary, an underlayer (not shown) maybe formed between the substrate 1 and the reflective film 2. Ifnecessary, an etching mask film (not shown) may be formed on thepattern-forming thin film 4.

Also in the above-mentioned mask blank 20 according to this embodiment,the reflective film which extends onto the end faces of the substrate 1when the reflective film 2 is formed on the main surface of thesubstrate 1 is a film of a single-layer structure in which thefilm-forming materials of the reflective film 2, for example, Si and Mo,are mixed and dispersed without any interface. Therefore, even if thetechnique of reducing adhesion of contamination using hydrogen radicalsor hydrogen plasma is applied during EUV exposure, it is possible tosignificantly reduce a risk of occurrence of blisters.

[Reflective Mask]

Next, description will be made of a reflective mask according to anembodiment of this disclosure.

The reflective mask according to this disclosure is characterized inthat a transfer pattern is formed in the pattern-forming thin film ofthe mask blank having the above-mentioned structure.

FIG. 4 is a sectional view for illustrating a structure of thereflective mask manufactured using the mask blank according to thisdisclosure. In FIG. 4 , parts equivalent to those in FIG. 1 or FIG. 3described above are designated by the same reference numerals.

The reflective mask 30 illustrated in FIG. 4 has the transfer pattern 4a formed by patterning the pattern-forming thin film 4 of theabove-mentioned mask blank 20 illustrated in FIG. 3 .

For example, photolithography is most preferable as a method ofpatterning the pattern-forming thin film 4 of the above-mentioned maskblank 20. Specifically, in order to obtain the reflective mask in thisdisclosure, it is preferable to use a manufacturing method at leastcomprising a step of forming a resist film on a surface of the maskblank 20 by using the above-mentioned mask blank 20, a step of forming aresist pattern in the resist film by electron beam writing anddevelopment, and a step of patterning the pattern-forming thin film 4 bydry etching with the resist pattern used as a mask.

Also in the above-described reflective mask 30 according to thisembodiment, the reflective film which extends onto the end faces of thesubstrate 1 when the reflective film 2 is formed on the main surface ofthe substrate 1 is a film of a single-layer structure in which thefilm-forming materials of the reflective film 2, for example, Si and Mo,are mixed and dispersed without any interface. Therefore, even if thetechnique of reducing adhesion of contamination using hydrogen radicalsor hydrogen plasma is applied during EUV exposure using the reflectivemask 30, it is possible to significantly reduce a risk of occurrence ofblisters.

[Method for Manufacturing Semiconductor Device]

This disclosure also provides a method for manufacturing a semiconductordevice, comprising a step of transferring by exposure a transfer patternonto a resist film on a semiconductor substrate using theabove-mentioned reflective mask.

By using the reflective mask according to this disclosure, even if thetechnique of reducing adhesion of contamination using hydrogen radicalsor hydrogen plasma is applied during EUV exposure, it is possible tosignificantly reduce a risk of occurrence of blisters. Thus, accordingto this disclosure, it is possible to perform excellent pattern transferand to manufacture a high-quality semiconductor device with ahigh-accuracy device pattern formed thereon.

EXAMPLES

Hereinafter, the embodiment of this disclosure will be described more indetail with reference to examples.

Example 1

A SiO₂—TiO₂-based glass substrate (having a size of about 152.4 mm×about152.4 mm and a thickness of about 6.35 mm) was prepared whose surfaceswere polished stepwise using a double-sided polishing device and ceriumoxide abrasive grains or colloidal silica abrasive grains andsurface-treated using low-concentration hydrofluosilicic acid. The glasssubstrate 1 thus obtained had surface roughness of 0.20 nm in root meansquare roughness (Rq). The surface roughness was measured by an atomicforce microscope (AFM) and a measurement area was 1 μm×1 μm.

Next, a conductive backside film (not shown) having a layered structureincluding a lower layer of CrON and an upper layer of CrN was formed ona main surface 1 b (main surface opposite from a main surface 1 a onwhich a reflective film 2 is to be formed) of the glass substrate 1. Thelower layer (CrON layer) was formed to a film thickness of 15 nm byreactive sputtering (DC magnetron sputtering) using a Cr target in anatmosphere of a mixture of an Ar gas, an N₂ gas, and an O₂ gas. Theupper layer (CrN layer) was formed to a film thickness of 180 nm byreactive sputtering (DC magnetron sputtering) using a Cr target in anatmosphere of a mixture of an Ar gas and an N₂ gas. The composition(atomic %) of the CrN layer was measured by X-ray photoelectronicspectroscopy (XPS). As a result, the atomic ratio was 91 atomic % forchromium (Cr) and 9 atomic % for nitrogen (N).

Next, on the main surface 1 a of the glass substrate 1, a reflectivefilm 2 (having a total film thickness of 280 nm) comprising a multilayerfilm including 40 periods of layers was formed by using an ion beamsputtering device where one period comprises a Si film (having a filmthickness of 4.2 nm) as a high refractive index layer and a Mo film(having a film thickness of 2.8 nm) as a low refractive index layer.Specifically, the conductive backside film of the glass substrate 1 wasfixed by an electrostatic chuck to a stage of the ion beam sputteringdevice. Sputtering particles (Si particles and Mo particles) wereincident to the main surface 1 a of the glass substrate 1 in an obliquedirection to be deposited on the main surface 1 a and the end faces 1 cand 1 d to form the reflective film 2. During the deposition, the endfaces 1 c and 1 d of the glass substrate 1 were not masked with a shieldor the like. Through the above-mentioned steps, a reflective film coatedsubstrate in Example 1 was obtained

The above-mentioned reflective film was not only formed on the mainsurface 1 a of the glass substrate 1 but also extends onto the end faces(four end faces including 1 c and 1 d) of the glass substrate 1. Thereflective film which extends onto the end faces of the glass substrate1 was analyzed using a transmission electron microscope (TEM). As aresult, it was confirmed that the film thickness (about 40 nm) of thereflective film 2 which extends onto the end faces was smaller than thefilm thickness of the reflective film 2 formed on the main surface 1 a.It was also confirmed that the reflective film on the end faces of theglass substrate 1 had a single-layer structure, not a multilayerstructure. Therefore, the reflective film on the end faces of the glasssubstrate 1 does not have a reflecting function for exposure light.Furthermore, the composition of the reflective film on the end faces ofthe glass substrate 1 was analyzed by an energy dispersive transmissionelectron microscope (TEM-EDX). As a result, it was confirmed that Si andMo mentioned above were contained. Thus, the reflective film spread overand adhered onto the end faces of the glass substrate 1 when thereflective film 2 was formed on the main surface 1 a of the glasssubstrate 1 was a film of a single-layer structure in which Si and Mo asfilm-forming materials of the reflective film 2 are mixed and dispersedwithout an interface.

The ratio L/(L+H) was equal to 0.25 where L represents the content[atomic %] of Mo contained in the reflective film which extends onto theend faces of the substrate 1 and being a main constituent element of thelow refractive index layers and H represents the content [atomic %] ofSi contained in the reflective film which extends onto the end faces ofthe substrate 1 and being a main constituent element of the highrefractive index layers. The surface roughness (root mean squareroughness) Rq of the reflective film which extends onto the end faceswas 2 nm or more.

Next, in the manner similar to that mentioned above, a conductivebackside film was formed on the main surface 1 b of the glass substrate1 and a reflective film comprising a multilayer film was formed bydepositing 40 periods of Si films and Mo films. Thus, a reflective filmcoated substrate was obtained.

Next, using a DC magnetron sputtering device, a protective film (havinga film thickness of 2.5 nm) of Ru and an absorber film comprising amultilayer film including a TaN film (having a film thickness of 48 nm,a composition of Ta:N=70 atomic %: 30 atomic %) and a TaO film (having afilm thickness of 11 nm and a composition of Ta:O=35 atomic %: 65 atomic%) were formed on the reflective film of the reflective film coatedsubstrate. Each composition was measured by X-ray photoelectronspectroscopy (XPS).

In the above-mentioned manner, the mask blank (reflective mask blank)was manufactured.

Next, using the above-mentioned mask blank, a reflective mask wasmanufactured.

At first, on a surface of the absorber film of the mask blank, apositive resist film for electron beam writing was formed as a resistfilm to a film thickness of 80 nm. The resist film was formed by spincoating using a spinner (spin coating device).

Next, after a predetermined mask pattern was written on theabove-mentioned resist film by an electron beam writer, development wasperformed to form a resist pattern.

Next, with the resist pattern used as a mask, the TaO film of theabsorber film was removed by etching using a fluorine-based gas (CF₄gas). The TaN film of the absorber film was removed by etching using achlorine-based gas (Cl₂ gas). Thus, an absorber film pattern was formed.

Furthermore, the resist pattern left on the absorber film pattern wasremoved by hot sulfuric acid to obtain the reflective mask for EUVlithography in Example 1. The reflective films 2 c and 2 d on the endfaces 1 c and 1 d of the reflective mask in Example 1 were observed. Asa result, it was confirmed that no distinct film reduction occurred.

In case where the reflective mask obtained as mentioned above is set inan EUV exposure device and pattern transfer is carried out onto asemiconductor substrate with a resist film formed thereon, it isdesired, for example, to fill the interior of an exposure chamber with ahydrogen atmosphere such as hydrogen radicals in order to reduceadhesion of contamination to a mirror or the mask in the exposure deviceduring EUV exposure, as described above. In case of the reflective maskin this example, as described above, the reflective film which extendsonto the end faces of the glass substrate when the reflective film isformed on the main surface of the glass substrate does not have amultilayer structure but is a film of a single-layer structure in whichSi and Mo as the film-forming materials of the reflective film are mixedand dispersed without an interface. Therefore, even if the technique ofreducing adhesion of contamination using hydrogen radicals or hydrogenplasma is applied during EUV exposure, it is possible to significantlyreduce a risk of occurrence of blisters. Therefore, excellent patterntransfer can be carried out according to this disclosure.

Comparative Example

In the manner similar to Example 1, a SiO₂—TiO₂-based glass substrate(having a size of about 152.4 mm×about 152.4 mm and a thickness of about6.35 mm) was prepared whose surfaces were polished stepwise using adouble-sided polishing device and cerium oxide abrasive grains orcolloidal silica abrasive grains and surface-treated usinglow-concentration hydrofluosilicic acid. The glass substrate 1 thusobtained had surface roughness of 0.25 nm in root mean square roughness(Rq). The surface roughness was measured by an atomic force microscope(AFM) and a measurement area was 1 μm×1 μm.

Next, in the manner similar to Example 1, a conductive backside film(not shown) having a layered structure including a lower layer of CrONand an upper layer of CrN was formed on a main surface 1 b of the glasssubstrate 1.

Next, on the main surface 1 a of the glass substrate 1, a reflectivefilm 2 (having a total film thickness of 280 nm) comprising a multilayerfilm including 40 periods of layers was formed by using an ALD (AtomicLayer Deposition) device (deposition device using atomic layerdeposition) where one period comprises a Si film (having a filmthickness of 4.2 nm) as a high refractive index layer and a Mo film(having a film thickness of 2.8 nm) as a low refractive index layer. Siparticles and Mo particles were incident to the main surface 1 a of theglass substrate 1 in an oblique direction to be deposited on the mainsurface 1 a and the end faces 1 c and 1 d to form the reflective film 2.During the deposition, the end faces 1 c and 1 d of the glass substrate1 were not masked with a shield or the like. Through the above-mentionedsteps, a reflective film coated substrate in Comparative Example wasobtained.

The above-mentioned reflective film was not only formed on the mainsurface of the glass substrate but also extends onto the end faces ofthe glass substrate. The structure of the reflective film on the endfaces of the glass substrate was analyzed using a transmission electronmicroscope (TEM). As a result, it was confirmed that the reflective filmon the end faces of the glass substrate had a multilayer structure,similar to the reflective film formed on the main surface, in which Sifilms and Mo films are alternately formed as layers. Thus, thereflective film spread over and adhered to the end faces of the glasssubstrate when the reflective film was formed on the main surface of theglass substrate was a film of a multilayer structure having aninterface.

Next, in the manner exactly same as that mentioned above, a conductivebackside film was formed on a main surface 1 b of another glasssubstrate 1. On a main surface 1 a, a reflective film comprising amultilayer film including 40 periods of Si films and Mo films was formedto obtain a reflective film coated substrate.

Next, in the manner similar to Example 1 mentioned above, a protectivefilm of Ru and an absorber film comprising a multilayer film including aTaN film and a TaO film were formed on the reflective film of thereflective film coated substrate to manufacture a mask blank (reflectivemask blank) of Comparative Example.

Next, using the mask blank, a reflective mask for EUV lithography inComparative Example was manufactured in the manner similar to Example 1mentioned above.

In case where the reflective mask obtained as mentioned above is set inan EUV exposure device and pattern transfer is carried out onto asemiconductor substrate with a resist film formed thereon, it is desiredto apply the technique of reducing adhesion of contamination usinghydrogen radicals or hydrogen plasma during EUV exposure. As describedabove, however, in the reflective mask according to Comparative Example,the reflective film which extends onto the end faces of the glasssubstrate has a multilayer structure with interfaces formed between therespective layers. Therefore, if the technique of reducing adhesion ofcontamination using hydrogen radicals or hydrogen plasma is appliedduring EUV exposure of the reflective mask in Comparative Example, arisk of occurrence of blisters at the end faces of the substrate isincreased to cause, for example, contamination in the interior of anexposure chamber. Accordingly, excellent pattern transfer is difficultto be carried out.

What is claimed is:
 1. A reflective film coated substrate comprising: asubstrate having: two main surfaces opposite from each other, and endfaces connected to outer edges of the two main surfaces; and areflective film formed on one of the main surfaces as a multilayerstructure comprising low refractive index layers and high refractiveindex layers alternately formed, wherein a content (atomic %) of a firstelement in the low refractive index layers is higher than a content(atomic %) of any other element in the low refractive index layers, anda content (atomic %) of a second element in the high refractive indexlayers is higher than a content (atomic %) of any other element in thehigh refractive index layers, the second element being a differentelement from the first element, and wherein the reflective film extendsonto the end faces as a single layer that contains the first element andthe second element.
 2. The reflective film coated substrate according toclaim 1, wherein, in the reflective film that extends onto the endfaces, a ratio of the content (atomic %) of the first element to thetotal content (atomic %) of the first element and the second element isless than 0.4.
 3. The reflective film coated substrate according toclaim 1, wherein the film thickness of the reflective film that extendsonto the end faces is smaller than the film thickness of the reflectivefilm formed on the main surface.
 4. The reflective film coated substrateaccording to claim 1, wherein the first element is molybdenum and thesecond element is silicon.
 5. The reflective film coated substrateaccording to claim 1, wherein the reflective film that extends onto theend faces has surface roughness (root mean square roughness) Rq of 1.5nm or more.
 6. A mask blank comprising: a substrate having: two mainsurfaces opposite from each other, and end faces connected to outeredges of the two main surfaces; a reflective film formed on one of themain surfaces as a multilayer structure comprising low refractive indexlayers and high refractive index layers alternately formed; and apattern-forming thin film formed on the reflective film, wherein acontent (atomic %) of a first element in the low refractive index layersis higher than a content (atomic %) of any other element in the lowrefractive index layers, and a content (atomic %) of a second element inthe high refractive index layers is higher than a content (atomic %) ofany other element in the high refractive index layers, the secondelement being a different element from the first element, and whereinthe reflective film extends onto the end faces as a single layer thatcontains the first element and the second element.
 7. The mask blankaccording to claim 6, wherein, in the reflective film that extends ontothe end faces, a ratio of the content (atomic %) of the first element tothe total content (atomic %) of the first element and the second elementis less than 0.4.
 8. The mask blank according to claim 6, wherein thefilm thickness of the reflective film that extends onto the end faces issmaller than the film thickness of the reflective film formed on themain surface.
 9. The mask blank according to claim 6, wherein the firstelement is molybdenum and the second element is silicon.
 10. The maskblank according to claim 6, wherein the reflective film that extendsonto the end faces has surface roughness (root mean square roughness) Rqof 1.5 nm or more.
 11. A reflective mask comprising: a substrate having:two main surfaces opposite to each other, and end faces connected toouter edges of the two main surfaces; a reflective film formed on one ofthe main surfaces as a multilayer structure comprising low refractiveindex layers and high refractive index layers alternately formed; and athin film formed on the reflective film and having a transfer pattern;wherein a content (atomic %) of a first element in the low refractiveindex layers is higher than a content (atomic %) of any other element inthe low refractive index layers, and a content (atomic %) of a secondelement in the high refractive index layers is higher than a content(atomic %) of any other element in the high refractive index layers, thesecond element being a different element from the first element, andwherein the reflective film extends onto the end faces as a single layerthat contains the first element and the second element.
 12. Thereflective mask according to claim 11, wherein, in the reflective filmthat extends onto the end faces, a ratio of the content (atomic %) ofthe first element to the total content (atomic %) of the first elementand the second element is less than 0.4.
 13. The reflective maskaccording to claim 11, wherein the film thickness of the reflective filmthat extends onto the end faces is smaller than the film thickness ofthe reflective film formed on the main surface.
 14. The reflective maskaccording to claim 11, wherein the first element is molybdenum and thesecond element is silicon.
 15. The reflective mask according to claim11, wherein the reflective film that extends onto the end faces hassurface roughness (root mean square roughness) Rq of 1.5 nm or more. 16.A method for manufacturing a semiconductor device, comprisingtransferring, by exposure, a transfer pattern onto a resist film on asemiconductor substrate by using the reflective mask according to claim11.